The present invention relates to a gas generator that can provide a controlled expansion and inflation of an airbag by burning gas generating agents in a housing by use of a plurality of ignitors.
A gas generator that works to expand and inflate the airbag rapidly to protect a vehicle occupant from the impact at a car collision is built in an airbag module fitted in a steering wheel or an instrument panel. The gas generator generates a large amount of gas rapidly by burning the gas generating agents by flames of the ignitors (squibs) ignited by the electrifying from control unit (control circuits).
The conventional gas generator has the mode of expanding and inflating the airbag rapidly at any time that the car collision happens, irrespective of a seating position of a vehicle occupant (a normal seat position or an abnormal seat position such as a stoop-shouldered position, etc.). Thus, the conventional gas generator has the problem of being unable to expand and inflate the airbag in accordance with the seating position of the occupant, such as, for example, the abnormal seat position of the occupant immediately behind the steering wheel or instrument panel.
Therefore, in recent years, there has been proposed and developed a gas generator for inflating the airbag in accordance with the seating position of the occupant, wherein an initial expansion of the airbag is moderated, for example.
As a technique to moderate the initial expansion of the airbag, there is known a gas generator (soft inflator) for expanding and inflating a passenger side airbag.
The proposed gas generator is so designed that an elongate cylindrical housing is partitioned into a plurality of combustion chambers and also the gas generating agents in the respective combustion chambers are burnt independently of each other by the respective ignitors (squibs).
The ignitors (squibs) are operated (ignited by electrifying thereto) with a time difference so that the gas generating agents in the respective combustion chambers are burnt successively. In the initial stage of inflation, the airbag is expanded and inflated gently or moderately by a small amount of gas generated in a first combustion chamber and then, is expanded and inflated rapidly by a large amount of gas generated in the respective combustion chambers.
This can provide a controlled expansion and inflation of the airbag, and as such can allow the airbag to be expanded and inflated in accordance with the seating position of the occupant.
However, in the conventional gas generator in which the gas generating agents are burnt by the plurality of ignitors, the ill-set of the connectors is likely to happen when connecting between the ignitors (squibs) and the control circuits (control units) for controlling the electrifying the ignitors.
The ill-set of the connectors causes the reversed operation of the ignitors (ignition by electrifying) and provides an inadequately controlled expansion and inflation of the airbag and thus reduced reliability.
It is the object of the present invention to provide a gas generator that can provide a controlled expansion and inflation of the airbag with improved reliability.
A gas generator of the present invention is so structured that gas generating agents in a housing are burnt by a plurality of ignitors, that the ignitors electrically ignite ignition agents by use of resistance exothermic bodies for generating heat by electrifying, and that resistance values thereof are differentiated from each other.
This enables the respective ignitors to be discriminated by applying the respective ignitors with weak electric current and measuring resistance value, voltage and the like, whereby the ill-connection can be discriminated and ignitor circuits can be connected properly.
Also, an amount of gas generated can be adjusted by adequately selecting the operation (ignition by electrifying) of the ignitors, whereby a controlled expansion and inflation of the airbag can be provided.
Also, a gas generator of the present invention is so structured that gas generating agents in a plurality of combustion chambers are burnt by a plurality of ignitors independently of each other, that the ignitors electrically ignite ignition agents by use of the resistance exothermic bodies for generating heat by electrifying, and that resistance values thereof are differentiated from each other.
This enables the respective ignitors to be discriminated by applying the respective ignitors with weak electric current and measuring resistance value and voltage, whereby the ill-set can be discriminated and ignitor circuits can be connected properly.
This can provide an adequately controlled expansion and inflation of the airbag, without reversing the operation order of the ignitors and the combustion order in the combustion chambers, and also can provide an improved reliability in the control.
In the present invention, it is possible to differentiate the resistance values of the resistance exothermic bodies by selecting a form or a material thereof.
A difference of resistance value between the respective ignitors is no less than 0.3 [xcexa9], preferably 0.6 to 2.0 [xcexa9], whereby the ignitors can be discriminated.